1. Field of the Invention
This invention relates to a zero load insertion type socket for an electric part having means for displacing a contact between a contacting position and a releasing position.
2. Brief Description of the Prior Art
A conventional socket as represented by U.S. Pat. No. 4,623,208 has a cantilevered arm which is integral with a contact and extends outwardly therefrom, and a curved spring portion likewise integral with the contact. The curved spring portion is compressed when the cantilevered arm is pushed down by a presser cover, to create an outward displacement as a component force, thereby separating a contacting portion of the contact from a contacting point of an IC, so that the IC can be inserted or removed with no-load.
In the prior art mentioned above, the necessary operating force for pushing down the pressure cover and the contacting force of the contact are determined by the spring portion of the contact.
Therefore, if a spring constant is set large in order to increase the contacting force, the necessary operating force is also increased. On the contrary, if a spring constant of the spring portion is set small in order to reduce the necessary operating force, the contacting force is also reduced. Thus, the prior art socket the inherent disadvantage that it is difficult to provide a design therefor which allows both the necessary operating force to be reduced as much as possible and the contacting force to be increased.
In a structure wherein a spring portion is compressed by pushing down a cantilevered arm in order to obtain an outward displacing motion, the amount of outward displacement caused by the downwardly directed force is very limited. Therefore, it is difficult to obtain outward displacement efficiently with respect to the amount of downward pressing necessary.
Additional problems are that when the cantilevered arm is pushed down, the axis of the contact tends to be twisted, which will likely result in a harmful displacement of the contacting portion, and metal fatigue tends to accumulate in the basal portion of the cantilevered arm because of repeated applications of external force in the bending direction.
Furthermore, the conventional contact is subjected to complicated and highly technical designing constraints, such as providing the cantilevered arm with a sectional area sufficient in order to give it a predetermined strength, establishing the above-mentioned spring constant, providing counter measures against twisting, and the like.